ALTER TABLE

Purpose

This statement is used to modify the structure of an existing table, such as altering the table and its attributes, adding columns, modifying columns and their attributes, and dropping columns.

Syntax

alter_table_stmt:
    ALTER TABLE table_name alter_table_action_list;

alter_table_action_list:
    alter_table_action [, alter_table_action ...]

alter_table_action:
      ADD [COLUMN] column_definition
          [ opt_position_column ]
    | ADD [COLUMN] (column_definition_list)
    | ADD [CONSTRAINT [constraint_name]] UNIQUE {INDEX | KEY}
          [index_name] index_desc
    | ADD [CONSTRAINT [constraint_name]] FOREIGN KEY
          [index_name] index_desc
          REFERENCES reference_definition
          [match_action][opt_reference_option_list]
    | ADD PRIMARY KEY (column_name)
    | ADD CONSTRAINT [constraint_name] CHECK (expression)[[NOT] ENFORCED]
    | ADD PARTITION (range_partition_list)
    | ADD {INDEX | KEY} [index_name] [index_type] (key_part,...) [index_option_list][index_column_group_option]
    | ADD FULLTEXT [INDEX | KEY] [index_name](column_name, [column_name ...]) [WITH PARSER tokenizer_option] [PARSER_PROPERTIES[=](parser_properties_list)] [FTS_INDEX_TYPE [=] {MATCH | PHRASE_MATCH}] [LOCAL]
    | ADD SEARCH INDEX [index_name] (search_index_column [, search_index_column ...])
    | ADD COLUMN GROUP([all columns, ]each column) [DELAYED]
    | ALTER [COLUMN] column_name {
          SET DEFAULT const_value
        | DROP DEFAULT
      }
    | ALTER {CHECK | CONSTRAINT} symbol [NOT] ENFORCED
    | ALTER INDEX index_name [VISIBLE | INVISIBLE] [STORAGE_CACHE_POLICY = {"hot"|"auto"|"none"}]
    | ALTER INDEX index_name
          [VISIBLE | INVISIBLE]
    | CHANGE [COLUMN] column_name column_definition
    | DROP [COLUMN] column_name [, DROP COLUMN column_name ...]
    | DROP {PARTITION | SUBPARTITION} partition_name_list
    | DROP TABLEGROUP
    | DROP FOREIGN KEY fk_name
    | DROP PRIMARY KEY [, ADD PRIMARY KEY (column)]
    | DROP CHECK constraint_name
    | DROP COLUMN GROUP([all columns, ]each column) [DELAYED]
    | DROP CLUSTERING KEY
    | MODIFY [COLUMN] column_definition
    | RENAME COLUMN old_col_name [TO|AS] new_col_name
    | RENAME [TO|AS] table_name
    | RENAME {INDEX | KEY} old_index_name [TO|AS] new_index_name
    | [SET] table_option_list
    | TRUNCATE {PARTITION | SUBPARTITION} partition_name_list
    | EXCHANGE PARTITION partition_name WITH TABLE origin_table_name WITHOUT VALIDATION
    | REORGANIZE PARTITION partition_name INTO (split_range_partition_list)
    | PARTITION BY {RANGE [COLUMNS]([column_name_list]) [SIZE('size_value')] [range_partition_list]
                   | partition_option}
    | PARTITION BY RANDOM SIZE('size_value')
    | MODIFY PARTITION partition_name ADD SUBPARTITION (add_subpartition_option)
    | ALTER {PARTITION | SUBPARTITION} partition_name STORAGE_CACHE_POLICY = {"hot" | "auto" | "none"}
    | FORCE
    | REMOVE TTL

column_definition_list:
    column_definition [, column_definition ...]

column_definition:
    column_name data_type
    [DEFAULT const_value] [AUTO_INCREMENT]
    [NULL | NOT NULL] [[PRIMARY] KEY] [UNIQUE [KEY]] [COMMENT string_value] [SKIP_INDEX(skip_index_option_list)] [ opt_position_column ]

skip_index_option_list:
    skip_index_option [,skip_index_option ...]

skip_index_option:
    MIN_MAX
    | SUM

opt_position_column:
    FIRST | BEFORE | AFTER column_name

index_desc:
   (column_desc_list) [index_type] [index_option_list]

match_action:
   MATCH {SIMPLE | FULL | PARTIAL}

opt_reference_option_list:
   reference_option [,reference_option ...]

reference_option:
   ON {DELETE | UPDATE} {RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT}

column_desc_list:
    column_desc [, column_desc ...]

column_desc:
     column_name [(length)] [ASC | DESC]

key_part:
    {index_col_name [(length)] | (expr)} [ASC | DESC]

search_index_column:
    column_name [WITH (search_col_option_list)]

search_col_option_list:
    [INCLUDE_PATHS = ('path1'[, 'path2']...)]
    [| EXCLUDE_PATHS = ('path1'[, 'path2']...)]
    [| INCLUDE_TYPES = (type1[, type2]...)]

index_type:
    USING BTREE

index_option_list:
    index_option [ index_option ...]

index_option:
     [GLOBAL | LOCAL]
    | block_size
    | compression
    | STORING(column_name_list)
    | COMMENT string_value
    | STORAGE_CACHE_POLICY (storage_cache_policy_option)

index_column_group_option:
    WITH COLUMN GROUP([all columns, ]each column)

tokenizer_option:
    SPACE
    | NGRAM
    | BENG
    | IK
    | NGRAM2

parser_properties_list:
    parser_properties, [parser_properties]

parser_properties:
    min_token_size = int_value
    | max_token_size = int_value
    | ngram_token_size = int_value
    | ik_mode = 'char_value'
    | min_ngram_size = int_value
    | max_ngram_size = int_value

table_option_list:
    table_option [ table_option ...]

table_option:
      TABLEGROUP = tablegroup_name
    | block_size
    | lob_inrow_threshold [=] num
    | compression
    | AUTO_INCREMENT [=] INT_VALUE
    | COMMENT string_value
    | parallel_clause
    | TABLE_MODE [=] 'table_mode_value'
    | MERGE_ENGINE [=] {partial_update | delete_insert | append_only}
    | AUTO_INCREMENT_CACHE_SIZE [=] INT_VALUE
    | READ {ONLY | WRITE}
    | DUPLICATE_SCOPE= 'none | cluster'
    | enable_macro_block_bloom_filter [=] {True | False}
    | DYNAMIC_PARTITION_POLICY [=] (dynamic_partition_policy_list)
    | SEMISTRUCT_ENCODING_TYPE [=] 'encoding' # Deprecated in V4.4.1. Use SEMISTRUCT_PROPERTIES instead.
    | SEMISTRUCT_PROPERTIES [=] (encoding_type=encoding|none[,freq_threshold=INT_VALUE])
    | STORAGE_CACHE_POLICY (storage_cache_policy_option)
    | CLUSTER BY (column_name_list)
    | HMS_CATALOG_NAME [=] string_value
    | COLUMN_NAME_CASE_SENSITIVE [=] {True | False}
    | DELTA_FORMAT [=] 'flat | encoding'
    | SKIP_INDEX_LEVEL [=] {1 | 0}
    | TTL [=] col_name + INTERVAL interval_num ttl_unit BY COMPACTION

parallel_clause:
    {NOPARALLEL | PARALLEL integer}

table_mode_value:
    NORMAL
    | QUEUING
    | MODERATE
    | SUPER
    | EXTREME

dynamic_partition_policy_list:
    dynamic_partition_policy_option [, dynamic_partition_policy_option ...]

dynamic_partition_policy_option:
    ENABLE = {true | false}
    | PRECREATE_TIME = {'-1' | '0' | 'n {hour | day | week | month | year}'}
    | EXPIRE_TIME = {'-1' | '0' | 'n {hour | day | week | month | year}'}

partition_option:
      PARTITION BY HASH(expression)
      [subpartition_option] PARTITIONS partition_count
    | PARTITION BY KEY([column_name_list])
      [subpartition_option] PARTITIONS partition_count
    | PARTITION BY RANGE {(expression) | COLUMNS (column_name_list)}
      [subpartition_option] (range_partition_list)

subpartition_option:
      SUBPARTITION BY HASH(expression)
      SUBPARTITIONS subpartition_count
    | SUBPARTITION BY KEY(column_name_list)
      SUBPARTITIONS subpartition_count
    | SUBPARTITION BY RANGE {(expression) | COLUMNS (column_name_list)}
      (range_subpartition_list)

storage_cache_policy_option:
    GLOBAL = {"hot" | "auto" | "cold" | "none"}
    | timeline_strategy_list

timeline_strategy_list:
    BOUNDARY_COLUMN = column_name
    | BOUNDARY_COLUMN_UNIT = {"s" | "ms"}
    | HOT_RETENTION = intnum retention_time_unit
    | MIXED_RETENTION = intnum retention_time_unit
    | GRANULARITY = {"partition" | "block"}

retention_time_unit:
    YEAR
    | MONTH
    | WEEK
    | DAY
    | HOUR
    | MINUTE

split_range_partition_list:
    PARTITION split_partition_name VALUES LESS THAN (value)
    [, PARTITION split_partition_name VALUES LESS THAN (value) ...]
     , PARTITION split_partition_name VALUES LESS THAN (source_value)

range_partition_list:
    range_partition [, range_partition ...]

range_partition:
    PARTITION partition_name
    VALUES LESS THAN {(expression_list) | MAXVALUE}
    [STORAGE_CACHE_POLICY = {"hot" | "auto" | "cold" | "none"}]

range_subpartition_list:
    range_subpartition [, range_subpartition ...]

range_subpartition:
    SUBPARTITION subpartition_name
    VALUES LESS THAN {(expression_list) | MAXVALUE}
    [STORAGE_CACHE_POLICY = {"hot" | "auto" | "cold" | "none"}]

expression_list:
    expression [, expression ...]

column_name_list:
    column_name [, column_name ...]

partition_name_list:
    partition_name [, partition_name ...]

partition_count | subpartition_count:
    INT_VALUE

add_subpartition_option:
    {SUBPARTITION subpartition_name VALUES LESS THAN range_partition_expr
        [, SUBPARTITION subpartition_name VALUES LESS THAN range_partition_expr] ...}
    | {SUBPARTITION subpartition_name VALUES IN list_partition_expr
        [, SUBPARTITION subpartition_name VALUES IN list_partition_expr] ...}

Parameters

table_mode_value

• NORMAL: The default value, indicating normal. In this mode, the probability of triggering a major compaction after a minor compaction is extremely low.
• QUEUING: In this mode, the probability of triggering a major compaction after a minor compaction is low.
• MODERATE: Indicates moderate. In this mode, the probability of triggering a major compaction after a minor compaction is medium.
• SUPER: Super. In this mode, a major compaction is triggered after a minor compaction with a high probability.
• EXTREME: Extreme. In this mode, the probability of triggering a major compaction after a minor compaction is higher.

For more information about major compactions, see Adaptive major compaction.

tokenizer_option

• SPACE: The default value, indicating that the text is split by spaces. You can specify the following properties:

  Attribute	Value range
  min_token_size	[1, 16]
  max_token_size	[10, 84]

• NGRAM: Indicates the word segmentation method based on N-gram (Chinese). The following attributes can be specified:

  Attribute	Value range
  ngram_token_size	[1, 10]

• NGRAM2: Indicates that the text is split into consecutive characters within the range of min_ngram_size to max_ngram_size. The following attributes can be specified:

  Attribute	Value range
  min_ngram_size	[1, 16]
  max_ngram_size	[1, 16]

• BENG: Indicates the Beng (basic English) tokenization method. You can specify the following properties:

  Attribute	Value range
  min_token_size	[1, 16]
  max_token_size	[10, 84]

• IK: Indicates the word segmentation method based on IK (Chinese). Currently, only the utf-8 character set is supported. The following attributes can be specified:

  Attribute	Value range
  ik_mode	smart max_word

You can use the TOKENIZE function to view the tokenization results of a text string using the specified tokenizer and JSON-formatted parameters.

parser_properties

• min_token_size: The minimum token length. Default value: 3. Value range: 1 to 16.

• max_token_size: The maximum token length. Default value: 84. Value range: 10 to 84.

• ngram_token_size: The token length for the NGRAM tokenizer. It is valid only for the NGRAM tokenizer. The default value is 2, and the value range is 1 to 10.

• ik_mode: the tokenization mode of the IK tokenizer. Valid values:

  • smart: The default value. The vocabulary in the dictionary is used to improve the accuracy of tokenization. The boundaries of the vocabulary in the dictionary are prioritized, which may reduce unnecessary extensions.
  • max_word: The vocabulary in the dictionary is identified, but it does not affect the maximum extension of tokenization. Even if the vocabulary is defined in the dictionary, the max_word mode still tries to split the text into more words.

• min_ngram_size: The minimum token length. The value range is [1, 16].

• max_ngram_size: The maximum token length. The value range is [1, 16].

Example:

1. Create table tbl1.

   CREATE TABLE tbl1 (col1 VARCHAR(200), col2 TEXT);
   

2. Add a full-text index fidx to table tbl1.

   ALTER TABLE tbl1 ADD FULLTEXT INDEX fidx(col2) WITH PARSER ik PARSER_PROPERTIES=(ik_mode='max_word');
   

dynamic_partition_policy_option

• ENABLE = {true | false}: Specifies whether to enable dynamic partition management. Valid values:

  • true: The default value. Indicates that dynamic partition management is enabled.
  • false: Indicates that dynamic partition management is disabled.

• PRECREATE_TIME = {'-1' | '0' | 'n {hour | day | week | month | year}'}: The precreation time. When dynamic partition management is scheduled, partitions are precreated so that the upper bound of the maximum partition > now() + precreate_time. Valid values:

  • -1: The default value. Indicates that no partitions are precreated.
  • 0: Indicates that only the current partition is precreated.
  • n {hour | day | week | month | year}: The time span for which partitions are precreated. For example, 3 hour indicates that partitions are precreated for the last 3 hours.

  Note

  • When multiple partitions are to be precreated, the interval between the boundaries of the partitions is TIME_UNIT.
  • The boundary of the first precreated partition is the ceiling of the upper bound of the existing maximum partition, rounded up to the nearest TIME_UNIT.

• EXPIRE_TIME = {'-1' | '0' | 'n {hour | day | week | month | year}'}: Optional. The partition expiration time. When dynamic partition management is scheduled, all partitions whose upper bound < now() - expire_time are deleted. Valid values:

  • -1: The default value. Indicates that partitions never expire.
  • 0: Indicates that all partitions except the current one have expired.
  • n {hour | day | week | month | year}: The partition expiration time. For example, 1 day indicates that the partition expires after 1 day.

For more information about modifying a dynamically partitioned table, see Modify a dynamically partitioned table.

Example:

ALTER TABLE tbl2 SET DYNAMIC_PARTITION_POLICY(
    ENABLE = true,
    PRECREATE_TIME = '1 day',
    EXPIRE_TIME = '-1'
);

storage_cache_policy

You do not need to pay attention to this parameter for now.

Examples

Add and drop columns

Create the sample table tbl1 and execute the DESCRIBE command to view its information.

obclient> CREATE TABLE tbl1 (c1 INT(11) PRIMARY KEY,c2 VARCHAR(50));
Query OK, 0 rows affected

obclient> DESCRIBE tbl1;
+-------+------------+----------+--------+---------+-------+
| Field | Type       | Null     | Key    | Default | Extra |
+-------+------------+----------+--------+---------+-------+
| c1    | int(11)    | NO       | PRI    | NULL    |       |
| c2    | varchar(50)| YES      |        | NULL    |       |
+-------+------------+----------+--------+---------+-------+

• Add the c3 column and execute the DESCRIBE command to view table information.

  obclient> ALTER TABLE tbl1 ADD c3 INT;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1;
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra |
  +-------+------------+----------+--------+---------+-------+
  | c1    | int(11)    | NO       | PRI    | NULL    |       |
  | c2    | varchar(50)| YES      |        | NULL    |       |
  | c3    | int(11)    | YES      |        | NULL    |       |
  +-------+------------+----------+--------+---------+-------+
  3 row affected
  

• Drop the c3 column and execute the DESCRIBE command to view the table information.

  obclient> ALTER TABLE tbl1 DROP c3;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1;
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra |
  +-------+------------+----------+--------+---------+-------+
  | c1    | int(11)    | NO       | PRI    | NULL    |       |
  | c2    | varchar(50)| YES      |        | NULL    |       |
  +-------+------------+----------+--------+---------+-------+
  2 row affected
  

• Rename the c2 column to c3 in table tbl1, and execute the DESCRIBE statement to view the table information.

  obclient> ALTER TABLE tbl1 CHANGE COLUMN c2 c3 VARCHAR(50);
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1;
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra |
  +-------+------------+----------+--------+---------+-------+
  | c1    | int(11)    | NO       | PRI    | NULL    |       |
  | c3    | varchar(50)| YES      |        | NULL    |       |
  +-------+------------+----------+--------+---------+-------+
  2 rows affected
  

• Add the c4 column to the tbl1 table and set it as the first column of the table. Then, execute the DESCRIBE command to view the table information.

  obclient> ALTER TABLE tbl1 ADD COLUMN c4 INTEGER FIRST;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1;
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra |
  +-------+------------+----------+--------+---------+-------+
  | c4    | int(11)    | YES      |        | NULL    |       |
  | c1    | int(11)    | NO       | PRI    | NULL    |       |
  | c3    | varchar(50)| YES      |        | NULL    |       |
  +-------+------------+----------+--------+---------+-------+
  3 row affected
  

• Add the c2 column after the c1 column and execute the DESCRIBE command to view the table information.

  obclient> ALTER TABLE tbl1 ADD COLUMN c2 INTEGER AFTER c1;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1;
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra |
  +-------+------------+----------+--------+---------+-------+
  | c4    | int(11)    | YES      |        | NULL    |       |
  | c1    | int(11)    | NO       | PRI    | NULL    |       |
  | c2    | int(11)    | YES      |        | NULL    |       |
  | c3    | varchar(50)| YES      |        | NULL    |       |
  +-------+------------+----------+--------+---------+-------+
  4 row affected
  

• Add the c5 column before the c4 column and execute the DESCRIBE command to view the table information.

  obclient> ALTER TABLE tbl1 ADD COLUMN c5 INT BEFORE c4;
  Query OK, 1 row affected
  
  obclient> DESCRIBE tbl1;
  +-------+------------+----------+--------+---------+-------+
  | Field | Type       | Null     | Key    | Default | Extra |
  +-------+------------+----------+--------+---------+-------+
  | c5    | int(11)    | YES      |        | NULL    |       |
  | c4    | int(11)    | YES      |        | NULL    |       |
  | c1    | int(11)    | NO       | PRI    | NULL    |       |
  | c2    | int(11)    | YES      |        | NULL    |       |
  | c3    | varchar(50)| YES      |        | NULL    |       |
  +-------+------------+----------+--------+---------+-------+
  5 row affected
  

• Add a foreign key constraint fk1 for table tbl2. When an UPDATE operation affects the key value in the parent table that matches a row in the subtable, perform a SET NULL operation.

  obclient> CREATE TABLE tbl2(c1 INT PRIMARY KEY,c2 INT);
  Query OK, 0 row affected
  obclient> CREATE TABLE tbl3(c1 INT PRIMARY KEY,c2 INT);
  Query OK, 0 row affected
  obclient> ALTER TABLE tbl2 ADD CONSTRAINT fk1 FOREIGN KEY (c2) REFERENCES tbl3(c1) ON UPDATE SET NULL;
  Query OK, 0 row affected
  

• Drop the foreign key constraint fk1 on table tbl3.

  obclient> ALTER TABLE tbl2 DROP FOREIGN KEY fk1;
  Query OK, 0 row affected
  

• Drop the primary key of table tbl2.

  obclient> ALTER TABLE tbl2 DROP PRIMARY KEY;
  Query OK, 0 row affected
  

Index operations

• Rename the ind1 index in the tbl2 table to ind2.

  obclient> CREATE TABLE tbl2(c1 INT(11) PRIMARY KEY,c2 INT(50));
  Query OK, 0 row affected
  
  obclient> CREATE INDEX ind1 ON tbl2 (c2 ASC);
  Query OK, 0 row affected
  obclient> ALTER TABLE tbl2 RENAME INDEX ind1 TO ind2;
  Query OK, 0 row affected
  

• Create index ind3 on table tbl2, referencing columns c1 and c2.

  obclient> ALTER TABLE tbl2 ADD INDEX ind3 (c1,c2);
  Query OK, 0 row affected
  

  You can execute the SHOW INDEX statement to view the created indexes.

  obclient> SHOW INDEX FROM tbl2;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
  | tbl2  |          0 | PRIMARY  |            1 | c1          | A         |        NULL | NULL     | NULL   |      | BTREE      | available |               | YES     |
  | tbl2  |          1 | ind2     |            1 | c2          | A         |        NULL | NULL     | NULL   |  YES | BTREE      | available |               | YES     |
  | tbl2  |          1 | ind3     |            1 | c1          | A         |        NULL | NULL     | NULL   |      | BTREE      | available |               | YES     |
  | tbl2  |          1 | ind3     |            2 | c2          | A         |        NULL | NULL     | NULL   |  YES | BTREE      | available |               | YES     |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+
  4 rows in set
  

• Drop the index ind2 on table tbl2.

  obclient> ALTER TABLE tbl2 DROP INDEX ind2;
  Query OK, 0 row affected
  

  Note

  In practical O&M scenarios, you can use the preceding method to achieve atomic index changes.

• Add three function-based indexes on t1_func. One is named i2, and the other two are automatically generated by the system, following the format of functional_index prefix plus a number.

  obclient> ALTER TABLE t1_func ADD INDEX ((CONCAT(c1,'a')));
  Query OK, 0 rows affected
  obclient> ALTER TABLE t1_func ADD INDEX ((c1+1));
  Query OK, 0 rows affected
  obclient> ALTER TABLE t1_func ADD INDEX i2 ((CONCAT(c1,'a')));
  Query OK, 0 rows affected
  obclient> SHOW CREATE TABLE t1_func;
  +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table   | Create Table                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
  +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | t1_func | CREATE TABLE `t1_func` (
  `c1` int(11) DEFAULT NULL,
  `c2` int(11) DEFAULT NULL,
  KEY `i1` (((`c1` + `c2`) < 1)) BLOCK_SIZE 16384 LOCAL,
  KEY `functional_index` (concat(`c1`,'a')) BLOCK_SIZE 16384 LOCAL,
  KEY `functional_index_2` ((`c1` + 1)) BLOCK_SIZE 16384 LOCAL,
  KEY `i2` (concat(`c1`,'a')) BLOCK_SIZE 16384 LOCAL
  ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
  +---------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set
  

• Create a columnstore index on the table.

  1. Execute the following SQL statement to create the tbl3 table.

     CREATE TABLE tbl3 (col1 INT, col2 VARCHAR(50));
     

  2. Create a columnstore index named idx1_tbl3 on the tbl3 table, referencing the col1 column.

     ALTER TABLE tbl3 ADD INDEX idx1_tbl3 (col1) WITH COLUMN GROUP(each column);
     

• Modified indexes are invisible.

  Note

  After an index is set to invisible, you can see the /*!80000 INVISIBLE */ marker in the table schema.

  1. Create table tbl4.

     CREATE TABLE tbl4 (col1 INT PRIMARY KEY, col2 INT, col3 INT);
     

  2. Create index idx1_tbl4.

     CREATE INDEX idx1_tbl4 ON tbl4(col2);
     

  3. The index idx1_tbl4 is modified and becomes invisible.

     ALTER TABLE tbl4 ALTER INDEX idx1_tbl4 INVISIBLE;
     

  4. View the structure of table tbl4 again.

     SHOW CREATE TABLE tbl4;
     

     The returned result is as follows:

     +-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
     | Table | Create Table                                                                                                                                                                                                                                                                                                                                                                                                              |
     +-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
     | tbl4  | CREATE TABLE `tbl4` (
       `col1` int(11) NOT NULL,
       `col2` int(11) DEFAULT NULL,
       `col3` int(11) DEFAULT NULL,
       PRIMARY KEY (`col1`),
       KEY `idx1_tbl4` (`col2`) BLOCK_SIZE 16384 LOCAL /*!80000 INVISIBLE */
     ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 WITH COLUMN GROUP(each column) |
     +-------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
     1 row in set
     

Specify the table-level cold/hot storage strategy for an index of an existing table

The syntax is as follows:

ALTER TABLE table_name ADD INDEX index_name(column_name)
    STORAGE_CACHE_POLICY (storage_cache_policy_option);

storage_cache_policy_option:
    GLOBAL = {"hot" | "auto" | "none"}
    | timeline_strategy_list

timeline_strategy_list:
    BOUNDARY_COLUMN = column_name
    | BOUNDARY_COLUMN_UNIT = {"s" | "ms"}
    | HOT_RETENTION = intnum retention_time_unit

retention_time_unit:
    YEAR
    | MONTH
    | WEEK
    | DAY
    | HOUR
    | MINUTE

Parameters

You can configure the cold/hot storage strategy for an index table.

• For a local index, you can specify the table-level STORAGE_CACHE_POLICY. If you do not specify the table-level STORAGE_CACHE_POLICY, it defaults to none, which means that the cold/hot storage strategy of the index partitions follows that of the data table.

• For a global index, you can specify the table-level STORAGE_CACHE_POLICY. If the index table is partitioned, you can also specify the partition-level STORAGE_CACHE_POLICY. If you do not specify the table-level STORAGE_CACHE_POLICY, it defaults to none.

  Note

  Starting from V4.4.1, if you do not specify the table-level STORAGE_CACHE_POLICY for a global index, the index follows the STORAGE_CACHE_POLICY of the primary table. If the primary table uses the Global strategy, the index follows the STORAGE_CACHE_POLICY of the primary table. If the primary table uses the TimeLine strategy, the index follows the hot strategy.

When you specify the table-level STORAGE_CACHE_POLICY, you define different attributes in the storage_cache_policy_option parameter in the Key-Value format. The attributes are described as follows:

• GLOBAL = {"hot" | "auto" | "cold" | "none"}: specifies the cold/hot storage strategy for the index data. Valid values:

  • hot: specifies the index as hot storage. If the cache disk space is sufficient, all data in the index table will be cached to the local cache disk.
  • auto: specifies the hot data of the index table to be automatically identified by the system.
  • cold: specifies the data of the index table as cold data. The data will not be cached to the local cache disk. For data that has been persisted to the cache, the system will actively trigger cache eviction. Subsequent accesses to the table data can be stored in the macroblock memory cache, but will not be persisted to the macroblock cache or microblock cache.
  • none: default value. The strategy of the index follows that of the primary table STORAGE_CACHE_POLICY.

• timeline_strategy_list: specifies the list of time-based strategies. Parameters are separated by commas. The system automatically adjusts data on the local cache disk based on the configured strategy.

  Note

  A timeline is a strategy that determines whether partition or macroblock data is hot based on time. When you use the timeline strategy, note the following:

  • Only Range-partitioned tables are supported. Range partitions can be at the primary or secondary level. Double Range partitions are not supported because it is unclear which Range partition to use for time-based expiration.
  • When you use the timeline strategy, the partition expression can only contain column names. Expressions are not supported. For example, PARTITION BY RANGE COLUMNS(expr(col3)) is not supported.
  • BOUNDARY_COLUMN must be a partition key. If the partition key consists of multiple columns, BOUNDARY_COLUMN must be the first column to determine whether the partition has expired.

  • BOUNDARY_COLUMN = column_name: specifies the column used to determine whether data is hot. Supported data types are integer types (BIGINT or INT, in the Unix timestamp format) and time types (TIMESTAMP, DATE, DATETIME, or YEAR).

    • If BOUNDARY_COLUMN is an integer type, the table can be partitioned by Range or Range Columns.
    • If BOUNDARY_COLUMN is a time type, the table can only be partitioned by Range Columns.

  • BOUNDARY_COLUMN_UNIT = {"s" | "ms"}: specifies the time unit for the BOUNDARY_COLUMN parameter. This parameter is only supported when BOUNDARY_COLUMN is an integer type. If the integer value is used as a timestamp, you must specify the timestamp unit. Otherwise, the system may misinterpret the timestamp. Valid values:

    • If the partition column is of the INT type, BOUNDARY_COLUMN_UNIT can only be s.
    • If the partition column is of the BIGINT type, BOUNDARY_COLUMN_UNIT can be s or ms.

  • HOT_RETENTION = intnum retention_time_unit: specifies the time range for hot data.

    • intnum: specifies an integer.

    • retention_time_unit: specifies the time unit. Valid values:

      • YEAR: specifies years.
      • MONTH: specifies months.
      • WEEK: specifies weeks.
      • DAY: specifies days.
      • HOUR: specifies hours.
      • MINUTE: specifies minutes.

Examples

• Create an index and specify the table-level STORAGE_CACHE_POLICY for the index.

  1. Create a table named tbl3.

     CREATE TABLE tbl3 (col1 INT, col2 INT, col3 INT);
     

  2. Create an index named idx1_tbl3 and specify the data of the index table as hot data.

     CREATE INDEX idx1_tbl3 ON tbl3 (col1) LOCAL 
         STORAGE_CACHE_POLICY (GLOBAL = "hot");
     

• Create an index and specify the data of the index table as hot data when you create the table.

  CREATE TABLE tbl4 (col1 INT, col2 INT,
      INDEX idx2 ((col1 + 1)) STORAGE_CACHE_POLICY (GLOBAL = "hot"), UNIQUE KEY ((col1 + col2)));
  

• Add an index to an existing table and specify the data of the index table as hot data.

  ALTER TABLE tbl4 ADD INDEX idx3(col1, col2) GLOBAL 
      STORAGE_CACHE_POLICY (GLOBAL = "hot");
  

Partition operations

• Truncate all data in partitions M202001 and M202002 of the partitioned table t_log_part_by_range.

  obclient> CREATE TABLE t_log_part_by_range (
      log_id      bigint NOT NULL
      , log_value varchar(50)
      , log_date  timestamp NOT NULL
  ) PARTITION BY RANGE(UNIX_TIMESTAMP(log_date))
  (
      PARTITION M202001 VALUES LESS THAN(UNIX_TIMESTAMP('2020/02/01'))
      , PARTITION M202002 VALUES LESS THAN(UNIX_TIMESTAMP('2020/03/01'))
      , PARTITION M202003 VALUES LESS THAN(UNIX_TIMESTAMP('2020/04/01'))
      , PARTITION M202004 VALUES LESS THAN(UNIX_TIMESTAMP('2020/05/01'))
      , PARTITION M202005 VALUES LESS THAN(UNIX_TIMESTAMP('2020/06/01'))
  );
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE t_log_part_by_range TRUNCATE PARTITION M202001, M202002;
  Query OK, 0 rows affected
  

• Add partition M202006 to the partitioned table t_log_part_by_range.

  obclient> CREATE TABLE t_log_part_by_range (
      log_id      bigint NOT NULL
      , log_value varchar(50)
      , log_date  timestamp NOT NULL
  ) PARTITION BY RANGE(UNIX_TIMESTAMP(log_date))
  (
      PARTITION M202001 VALUES LESS THAN(UNIX_TIMESTAMP('2020/02/01'))
      , PARTITION M202002 VALUES LESS THAN(UNIX_TIMESTAMP('2020/03/01'))
      , PARTITION M202003 VALUES LESS THAN(UNIX_TIMESTAMP('2020/04/01'))
      , PARTITION M202004 VALUES LESS THAN(UNIX_TIMESTAMP('2020/05/01'))
      , PARTITION M202005 VALUES LESS THAN(UNIX_TIMESTAMP('2020/06/01'))
  );
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE t_log_part_by_range ADD PARTITION
           (PARTITION M202006 VALUES LESS THAN(UNIX_TIMESTAMP('2020/07/01'))
           );
  

Change the cold/hot storage strategy of an index table

You can use the ALTER TABLE statement to change the cold/hot storage strategy (STORAGE_CACHE_POLICY) of an existing index table. The syntax is as follows:

ALTER TABLE table_name ALTER INDEX STORAGE_CACHE_POLICY (storage_cache_policy_option);

storage_cache_policy_option:
    GLOBAL = {"hot" | "auto" | "none"}
    | timeline_strategy_list

timeline_strategy_list:
    | BOUNDARY_COLUMN = column_name
    | BOUNDARY_COLUMN_UNIT = {"s" | "ms"}
    | HOT_RETENTION = intnum retention_time_unit

retention_time_unit:
    YEAR
    | MONTH
    | WEEK
    | DAY
    | HOUR
    | MINUTE

Parameter description

• GLOBAL = {"hot" | "auto" | "none"}: specifies the cold/hot storage strategy for the data of the index table. Valid values:

  • hot: specifies that the data of the index table is stored in hot storage. If the cache disk space is sufficient, all data in the index table will be cached to the local cache disk.
  • auto: specifies that the system automatically identifies the hot data of the index table.
  • none: the default value. This option indicates that the cold/hot storage strategy of the index table follows that of the primary table, specified by the STORAGE_CACHE_POLICY parameter.

• timeline_strategy_list: specifies the list of time-axis strategy parameters. The parameters are separated by commas. The time-axis strategy enables the system to automatically adjust the data on the local cache disk based on the configured strategy. The system determines whether to store the data of a partition or macroblock in hot storage based on the time.

  Note

  A time-axis strategy is based on the partition range defined by the RANGE partitioning. The system caches the hot data of a partition when the specified time condition is met. When you use a time-axis strategy, note the following:

  • A time-axis strategy is supported only for RANGE-partitioned tables (RANGE partitioning can be at the primary or secondary level). This is because the system needs to determine whether the data has expired based on time. However, a double RANGE partitioning is not supported because the system cannot determine which RANGE partition to use for time-based expiration.
  • When you use a time-axis strategy, the partition expression can contain only column names. Expressions are not supported. For example, PARTITION BY RANGE COLUMNS(expr(col3)) is invalid.
  • BOUNDARY_COLUMN must be a partition key. If the partition key contains multiple columns, BOUNDARY_COLUMN must be the first column, which is used to determine whether the partition has expired.

  • BOUNDARY_COLUMN = column_name: specifies the column used to determine the hot data. Supported data types: integer (BIGINT or INT, in the format of a Unix timestamp) and time (TIMESTAMP, DATE, DATETIME, or YEAR).

    • If the data type of BOUNDARY_COLUMN is an integer, the table can be partitioned by RANGE or RANGE COLUMNS.
    • If the data type of BOUNDARY_COLUMN is a time type, the table can be partitioned only by RANGE COLUMNS.

  • BOUNDARY_COLUMN_UNIT = {"s" | "ms"}: specifies the time unit of the BOUNDARY_COLUMN parameter. This parameter is supported only when the data type of BOUNDARY_COLUMN is an integer. If the integer value is used as a timestamp, you must specify the timestamp unit to avoid incorrect parsing. Valid values:

    • If the partition column is of the INT type, BOUNDARY_COLUMN_UNIT can be only s.
    • If the partition column is of the BIGINT type, BOUNDARY_COLUMN_UNIT can be s or ms.

  • HOT_RETENTION = intnum retention_time_unit: specifies the time range for hot data.

    • intnum: specifies an integer.

    • retention_time_unit: specifies the time unit. Valid values:

      • YEAR: specifies years.
      • MONTH: specifies months.
      • WEEK: specifies weeks.
      • DAY: specifies days.
      • HOUR: specifies hours.
      • MINUTE: specifies minutes.

Example

Configure the system to automatically identify the hot data of the index table idx2.

ALTER TABLE test_tbl2 ALTER INDEX idx2
    STORAGE_CACHE_POLICY (GLOBAL = "auto");

Change the parallelism

• Change the parallelism of the table tbl3 to 2.

  obclient> ALTER TABLE tbl3 PARALLEL 2;
  

  You can also use the PARALLEL hint to change the parallelism of a table. The syntax is as follows: alter /*+ parallel(int) */ table.

Column type operations

• Modify the regular column col1 of table tbl4 to an auto-increment column.

  obclient> CREATE TABLE tbl4 (col1 BIGINT(10) NOT NULL,col2 INT);
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl4 MODIFY col1 BIGINT(10) AUTO_INCREMENT;
  Query OK, 0 rows affected
  

• Add a primary key col1 for table tbl4, and then change the primary key to col2.

  obclient> ALTER TABLE tbl4 ADD PRIMARY KEY (col1);
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl4 DROP PRIMARY KEY,ADD PRIMARY KEY (`col2`);
  Query OK, 0 rows affected
  

• Added a CHECK constraint.

  obclient> CREATE TABLE tbl7(col1 VARCHAR(10),col2 VARCHAR(10));
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl7 ADD CONSTRAINT my_check CHECK (col1> col2) ;
  Query OK, 0 rows affected
  

• Drop the CHECK constraint on table tbl7.

  obclient> ALTER TABLE tbl7 DROP CHECK my_check;
  Query OK, 0 rows affected
  

• Change the column type to NOT NULL.

  obclient> CREATE TABLE dept(
      deptno           NUMBER(2,0),
      dname            VARCHAR(14),
      location         VARCHAR(13),
      CONSTRAINT pk_dept PRIMARY KEY(deptno)
  );
  Query OK, 0 rows affected
  
  obclient> CREATE TABLE emp(
      empno         NUMBER(4,0) NOT NULL,
      empname       VARCHAR(10) NOT NULL,
      job           VARCHAR(9) NOT NULL,
      mgr           NUMBER(4,0) NOT NULL,
      hiredate      DATE NOT NULL,
      sal           NUMBER(7,2) DEFAULT NULL,
      comm          NUMBER(7,2) DEFAULT NULL,
      deptno        NUMBER(2,0) DEFAULT NULL,
      CONSTRAINT PK_emp PRIMARY KEY (empno),
      CONSTRAINT FK_deptno  FOREIGN KEY (deptno)  REFERENCES dept (deptno)
  );
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE emp MODIFY deptno NUMBER(2,0) DEFAULT '12' NOT NULL;
  Query OK, 0 rows affected
  

Change column name and add a NOT NULL column constraint

obclient> ALTER TABLE test_alter1 MODIFY COLUMN `C1` varchar(10) NOT NULL;
Query OK, 0 rows affected (2.421 sec)

Add NOT NULL constraints to both columns simultaneously

Run the following command to add a NOT NULL constraint on both columns C1 and C2:

obclient> ALTER TABLE test_alter4 MODIFY COLUMN c1 varchar(10) NOT NULL, MODIFY COLUMN c2 varchar(10) NOT NULL;
Query OK, 0 rows affected (2.605 sec)

Change the type of a column with a prefix index

1. Execute the following statement to create a table named test_alter5 that contains a column named c1 of the CHAR(20) data type and has a prefix index named idx_c1 on the c1 column:

   obclient> CREATE TABLE test_alter5 (c1 char(20), KEY idx_c1(c1(10)));
   

2. Run the following command to modify the data type of column c1 to varchar(20):

   obclient> ALTER TABLE test_alter5 MODIFY COLUMN c1 varchar(20);
   

Change a foreign key constraint rule

1. Run the following command to create table t1 and add a unique constraint on the integer column c1:

   obclient> CREATE TABLE t1(c1 int unique key);
   

2. Execute the following command to create a table named t2, which contains an integer column c1, and define a foreign key constraint:

   obclient> CREATE TABLE t2(c1 int, CONSTRAINT fk_cst_test FOREIGN KEY (c1) REFERENCES t1(c1) on update set null on delete no action);
   

3. Execute the following statement to query the INFORMATION_SCHEMA.REFERENTIAL_CONSTRAINTS system table and obtain the update and delete rules of the foreign key constraint named fk_cst_test:

   obclient> SELECT update_rule, delete_rule FROM information_schema.referential_constraints WHERE CONSTRAINT_NAME = 'fk_cst_test';
   

   The return result is as follows:

   +-------------+-------------+
   | update_rule | delete_rule |
   +-------------+-------------+
   | SET NULL    | NO ACTION   |
   +-------------+-------------+
   

   • UPDATE_RULE: SET NULL is returned, which indicates that the foreign key is set to NULL during an update.
   • DELETE_RULE: NO ACTION is returned, which indicates that the constraint is checked during a deletion, and the operation may be blocked.

Rename a column

• The RENAME COLUMN statement does not change the column definition, only its name. If the target name already exists in the table, the RENAME COLUMN operation will report an error; however, renaming to the original name will not cause an error.

  obclient> CREATE TABLE tbl8 (a INT, b INT);
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl8 RENAME COLUMN a TO b;
  ERROR 1060 (42S21): Duplicate column name 'b'
  
  obclient> ALTER TABLE tbl8 RENAME COLUMN a TO a;
  Query OK, 0 rows affected
  

• If an index exists on the renamed column, the RENAME COLUMN statement can be executed normally and the index definition will be automatically cascaded.

  obclient> CREATE TABLE tbl9 (a INT, b INT, index idx_a(a));
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM tbl9;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | tbl9  |          1 | idx_a    |            1 | a           | A         |        NULL | NULL     | NULL   | YES  | BTREE      | available |               | YES     | NULL       |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  1 row in set
  
  obclient> ALTER TABLE tbl9 RENAME COLUMN a TO c;
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM tbl9;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | tbl9  |          1 | idx_a    |            1 | c           | A         |        NULL | NULL     | NULL   | YES  | BTREE      | available |               | YES     | NULL       |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  1 row in set
  

• If a renamed column is referenced by a prefix index, the RENAME COLUMN statement can be executed normally, as prefix indexes support cascade modification.

  DROP TABLE tbl9;
  obclient> CREATE TABLE tbl9 (c1 INT PRIMARY KEY, c2 BLOB, c3 INT, INDEX i1 (c2(10)));
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl9 RENAME COLUMN c2 TO c2_, RENAME COLUMN c1 TO c2_1;
  DESC tbl9;
  Query OK, 0 rows affected
  
  obclient> SHOW INDEX FROM tbl9;
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment   | Index_comment | Visible | Expression |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  | tbl9  |          0 | PRIMARY  |            1 | c2_1        | A         |        NULL | NULL     | NULL   |      | BTREE      | available |               | YES     | NULL       |
  | tbl9  |          1 | i1       |            1 | c2_         | A         |        NULL | 10       | NULL   | YES  | BTREE      | available |               | YES     | NULL       |
  +-------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+-----------+---------------+---------+------------+
  2 rows in set
  

• If a foreign key constraint is created on the renamed column, the RENAME COLUMN statement can be executed normally, and the foreign key constraint will be automatically updated.

  obclient> CREATE TABLE tbl10 (a INT PRIMARY KEY);
  Query OK, 0 rows affected
  
  obclient> CREATE TABLE tbl11(b INT, FOREIGN KEY (b) REFERENCES tbl10(a));
  
  obclient> SHOW CREATE TABLE tbl11;
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table | Create Table                                                                                                                                                                                                                                                                                                                                                      |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | tbl11 | CREATE TABLE `tbl11` (
  `b` int(11) DEFAULT NULL,
  CONSTRAINT `tbl11_OBFK_1694681944513338` FOREIGN KEY (`b`) REFERENCES `test`.`tbl10`(`a`) ON UPDATE RESTRICT ON DELETE RESTRICT
  ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE =  16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set
  
  obclient> ALTER TABLE tbl10 RENAME COLUMN a TO c;
  Query OK, 0 rows affected
  
  obclient> SHOW CREATE TABLE tbl11;
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | Table | Create Table                                                                                                                                                                                                                                                                                                                                                      |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  | tbl11 | CREATE TABLE `tbl11` (
  `b` int(11) DEFAULT NULL,
  CONSTRAINT `tbl11_OBFK_1694681944513338` FOREIGN KEY (`b`) REFERENCES `test`.`tbl10`(`c`) ON UPDATE RESTRICT ON DELETE RESTRICT
  ) DEFAULT CHARSET = utf8mb4 ROW_FORMAT = DYNAMIC COMPRESSION = 'zstd_1.3.8' REPLICA_NUM = 1 BLOCK_SIZE = 16384 USE_BLOOM_FILTER = FALSE TABLET_SIZE = 134217728 PCTFREE = 0 |
  +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
  1 row in set
  

OceanBase Database does not support modification or automatic cascading modification in the following scenarios:

• If a renamed column is referenced by a generated list expression, the column name cannot be modified; otherwise, an error will occur during execution.

  obclient> CREATE TABLE tbl12(a INT, b INT AS (a + 1), c INT, d INT, CONSTRAINT d_check CHECK(d > 0)) PARTITION BY HASH(c + 1) PARTITIONS 2;
  
  obclient> ALTER TABLE tbl12 RENAME COLUMN a TO e;
  ERROR 3108 (HY000): Column 'a' has a generated column dependency
  

• If the renamed column is referenced by a partitioning expression, the column name cannot be modified, and an error will be returned.

  obclient> ALTER TABLE tbl12 RENAME COLUMN c TO e;
  ERROR 3855 (HY000): Column 'c' has a partitioning function dependency and cannot be dropped or renamed.
  

• If the renamed column is referenced by a CHECK constraint, the column name cannot be modified, and an error will be returned.

  obclient> ALTER TABLE tbl12 RENAME COLUMN d TO e;
  ERROR 3959 (HY000): Check constraint 'd_check' uses column 'd', hence column cannot be dropped or renamed.
  

• If a renamed column is referenced by a function-based index, the column name cannot be modified; otherwise, an error will occur during execution.

  DROP TABLE IF EXISTS tbl12;
  obclient> CREATE TABLE tbl12(i INT, INDEX ((i+1)));
  Query OK, 0 rows affected
  
  obclient> ALTER TABLE tbl12 RENAME COLUMN i TO j;
  ERROR 3837 (HY000): Column 'i' has a functional index dependency and cannot be dropped or renamed.
  

• If the renamed column is referenced by a view, the RENAME COLUMN statement will execute successfully, but querying the view will return an error. You need to manually modify the view definition.

  obclient> CREATE TABLE tbl13(a INT);
  Query OK, 0 rows affected
  
  obclient> CREATE VIEW v1 AS SELECT a + 1 FROM tbl13;
  Query OK, 0 rows affected
  
  obclient> SELECT * FROM v1;
  Empty set
  
  obclient> ALTER TABLE tbl13 RENAME COLUMN a TO b;
  Query OK, 0 rows affected
  
  obclient> SELECT * FROM v1;
  ERROR 1356 (42S22): View 'test.v1' references invalid table(s) or column(s) or function(s) or definer/invoker of view lack rights to use them
  

• A renamed column is referenced by a stored procedure. The RENAME COLUMN statement executes successfully, but the CALL procedure reports an error, requiring manual modification by the user.

  obclient> CREATE TABLE tbl14(a INT);
  Query OK, 0 rows affected
  
  obclient> CREATE PROCEDURE proc() SELECT a + 1 FROM tbl14;
  Query OK, 0 rows affected
  
  obclient> CALL proc();
  Empty set
  
  obclient> ALTER TABLE tbl14 RENAME COLUMN a TO b;
  Query OK, 0 rows affected
  
  obclient> CALL proc();
  ERROR 1054 (42S22): Unknown column 'a' in 'field list'
  

Modify the columnar storage attributes of a table

1. Run the following SQL statement to create a table named tbl1.

   CREATE TABLE tbl1 (col1 INT PRIMARY KEY, col2 VARCHAR(50));
   

2. Change the table tbl1 to a rowstore-redundant table and then delete the rowstore-redundant attribute.

   ALTER TABLE tbl1 ADD COLUMN GROUP(all columns, each column);
   

   ALTER TABLE tbl1 DROP COLUMN GROUP(all columns, each column);
   

3. Change table tbl1 to a columnar storage table, and then drop the columnar storage attribute.

   ALTER TABLE tbl1 ADD COLUMN GROUP(each column);
   

   ALTER TABLE tbl1 DROP COLUMN GROUP(each column);
   

Modify the skip index attribute of a column

Use the following SQL statement to create the table test_skidx.

CREATE TABLE test_skidx(
  col1 INT SKIP_INDEX(MIN_MAX, SUM),
  col2 FLOAT SKIP_INDEX(MIN_MAX),
  col3 VARCHAR(1024) SKIP_INDEX(MIN_MAX),
  col4 CHAR(10)
  );

• Modify the Skip Index attribute of the col2 column in the test_skidx table to the SUM Skip Index type.

  ALTER TABLE test_skidx MODIFY COLUMN col2 FLOAT SKIP_INDEX(SUM);
  

• Add the Skip Index attribute to a new column after the table is created. Add the MIN_MAX Skip Index type to the col4 column in the test_skidx table.

  ALTER TABLE test_skidx MODIFY COLUMN col4 CHAR(10) SKIP_INDEX(MIN_MAX);
  

• Drop a column after table creation with the SKIP INDEX clause. Drop the col1 column from the test_skidx table using the SKIP INDEX clause.

  ALTER TABLE test_skidx MODIFY COLUMN col1 INT SKIP_INDEX();
  

  or

  ALTER TABLE test_skidx MODIFY COLUMN col1 INT;
  

Modify table attributes

Disable the persistent macroblock-level Bloom filter for the tb table.

ALTER TABLE tb SET enable_macro_block_bloom_filter = False;

Modify the STORAGE_CACHE_POLICY at the table level

• Enable the system to automatically identify hot data for the tbl1 table.

  ALTER TABLE tbl1 SET STORAGE_CACHE_POLICY (GLOBAL = "auto");
  

• Enable the system to automatically identify hot data for the tbl2 table based on the col3 column, where the data is within 2 months of the current time.

  ALTER TABLE tbl2 SET STORAGE_CACHE_POLICY (BOUNDARY_COLUMN = col3, HOT_RETENTION = 2 MONTH); 
  

Modify the STORAGE_CACHE_POLICY at the partition level

• Add a partition named p2 to the tbl3 table. Enable the system to automatically identify hot data for the p2 partition, which needs to be cached to the local disk.

  ALTER TABLE tbl3 ADD PARTITION (PARTITION p2 VALUES LESS THAN(300) STORAGE_CACHE_POLICY = "auto");
  

• Enable the system to automatically identify hot data for the existing partition p1 in the tbl3 table.

  ALTER TABLE tbl3 ALTER PARTITION p1 STORAGE_CACHE_POLICY = 'hot';
  

• Enable the system to automatically identify hot data for the sp3 subpartition in the tbl4 table, which needs to be cached to the local disk.

  ALTER TABLE tbl4 ALTER SUBPARTITON sp3 STORAGE_CACHE_POLICY = 'auto';
  

Modify or delete the TTL policy of a table

• Modify the TTL policy of a table. For example, set the data expiration time to 1 hour.

  obclient(root@mysql001)[infotest]> ALTER TABLE tbl5 SET TTL payment_time + INTERVAL 1 HOUR BY COMPACTION;
  

5. Delete the table's TTL attribute.

   obclient(root@mysql001)[infotest]> ALTER TABLE tbl5 REMOVE TTL;
   

References

• Modify a table

• Use the TTL (Time To Live) feature